In light source devices for liquid crystal projectors and DLP projectors which are required to be reduced in size and provide bright projection images, short arc type high pressure mercury vapor discharge lamps which are small in size and can provide light emission at high brightness have been used as the light source. Since the lamps of this type involve a problem that starting performance under cold condition and restarting performance are not generally preferred under hot restrike condition, start assisting light sources are provided to enhance the starting performance.
A light source device shown in FIG. 13 has a discharge tube 80 that radiates a UV-light to a discharge chamber 54 of a high pressure discharge lamp 51 upon starting lighting is disposed (refer to Patent Document 1).
The high pressure discharge lamp 51 has a discharge chamber 54 disposed in a central portion of an arc tube 52 comprising a quartz glass tube where a pair of tungsten electrodes 56, 56 are opposed to each other at a short inter-electrode distance of about 1 mm, a starting gas such as mercury and a halogen, for example, bromine and an argon gas is filled, and a pair of electrode sealed portions 59R, 59L encapsulating an electrode 56, a metal foil 57, and an electrode lead 58 from the discharge chamber 54 to both ends of the arc tube 52 and is connected to a lighting circuit by way of electrode leads 58, 58 protruding from end faces of the electrode sealed portions 59R, 59L.
Then, the high pressure discharge lamp 51 is integrally attached to a concave reflector 81 by inserting an electrode sealed portion 59L on one side through a bottom hole 83 formed in the bottom of the concave reflector 81, and a glow discharge tube 80 is disposed as an auxiliary, a start of the light source for radiating the UV-light enhancing the starting performance of the lamp 51 upon starting of lighting to the discharge chamber 54.
Further, since the glow discharge lamp 80 has a simple structure of sealing since a rare gas such as an argon gas containing mercury vapor inside a glass seal tube 84 comprising quartz glass, an internal electrode 85 comprising a metal foil having a pair of lead wires 86, 86 protruding from both ends of the glass seal tube 84, and forming a coiled external electrode 87 by winding a chromium-aluminum iron alloy wire 89 of about 0.2 mm diameter around the outer periphery of the glass seal tube 84, it has an advantage that the manufacturing cost is not increased.
The internal electrode 85 and the external electrode 87 of the glow discharge tube 80 are connected respectively to one polar side 88R and the other polar side 88L of the lamp lighting circuit and, when a starting high frequency pulse voltage is applied between the internal electrode 85 and the external electrode 87, glow discharge occurs in the mercury vapor sealed in the glass seal tube 84 as the main body of the discharge tube 80 to generate the UV-light, and a portion of the UV-light is radiated directly through a vent hole 82 for cooling air formed in the reflector 81 to the discharge chamber 54 of the lamp 51 disposed inside the reflector 81, or radiated by reflection on the reflection surface of the reflector 81.
However, in a case of forming the coiled external electrode 87 is disposed at the outer periphery of the glass seal tube, when the number of turns of coils is small, since the generation amount of the UV-light from the discharge tube 80 is small, no necessary and sufficient amount of the UV-light can be radiated to the discharge chamber 54 of the lamp 51. Further, when the number of turns of the coiled external electrode 87 is increased, the UV-light is shielded by the external electrode 87 and a necessary and sufficient amount of the UV-light cannot be radiated to the discharge chamber 54 of the lamp 51.
Further, the discharge tube 80 is held at a predetermined position by connecting the lead 86 of the internal electrode 85 of the discharge tube 80, and the coiled external electrode 87 to one polar side 88R and the other polar side 88L of the lamp lighting circuit. When both electric connection and mechanical holding for the discharge tube 80 are intended by the connection of the lead and the coils, this results in a problem that positioning for the discharge tube 80 is difficult and in a case of providing fixing means additionally, the structure is complicated.